Why Onions Deserve Garden Space
Onions look humble, yet no kitchen runs without them. One 3×8 ft bed can supply a family of four for an entire year, and the crop stores at room temperature while most vegetables demand freezer space or constant electricity. Few edibles give so much flavor for so little work.
Choosing the Right Type for Your Latitude
Onions are classified by day length—how many daylight hours trigger bulb formation. Choose wrong and you will grow scallion-sized plants that never swell.
Long-day varieties (14–16 h daylight) suit zones 3–6; try ‘Walla Walla’ or ‘Yellow Sweet Spanish’.
Intermediate-day (12–14 h) fit the mid-section; ‘Candy’ is forgiving and sweet.
Short-day (10–12 h) work only in mild winter regions; ‘Texas Grano’ and ‘Red Creole’ are supermarket staples from the South.
Sets, Seeds, or Transplants?
Sets (tiny dormant bulbs) are the fast lane: plant, water, wait. They tolerate light frost, making them perfect for beginners, though choice of varieties is limited.
Seeds give the widest selection and are cheapest, but they need 8–10 weeks indoors under lights before the last frost. Thinning is essential.
Transplants (bundled seedlings) bridge the gap—already pencil-thick, they skip indoor work yet offer heirloom types. Buy them only if roots look white and tops are bright green.
Preparing the Bed
Onions are greedy for sunshine, potassium, and phosphorus but modest on nitrogen; too much nitrogen encourages lush tops and small bulbs. Aim for a loose, friable soil pH 6.2–6.8.
1. Work the bed 10 in deep in fall or two weeks before planting.
2. Mix in 1 in of finished compost and a light dusting of bone meal (follow label).
3. Rake the surface flat; stones or clods distort bulbs.
When to Plant Outdoors
Soil should be 50 °F and workable. A cold frame or low tunnel lets you cheat by two weeks. Long-day onions need the longest season; short-day types can go in during late fall for an early-spring harvest.
Spacing & Depth Cheat-Sheet
Sets: 1 in deep, pointy end up, 4 in apart in rows 12 in apart.
Seeds: ½ in deep, 2 in apart, then thin to 4 in.
Transplants: Set so white base is just under soil line at same 4 in spacing.
Close spacing yields scallions; wide spacing (6 in) gives colossal bulbs but fewer per foot.
Watering the Right Way
Onions have sparse, shallow roots. Consistent moisture during the first 6 weeks grows large leaves; more leaves equals more rings in the bulb.
Rule of thumb: 1 in of water weekly from rain or irrigation. Switch to every 10 days once necks start softening to prevent rot. Always water at soil level—wet foliage invites fungal leaf spot.
Feeding Schedule
Week 3: Side-dress with blood meal or composted poultry manure (¼ cup per 10 ft row).
Week 6: A second, lighter feeding if leaf color pales.
Stop all nitrogen when you see the first bulb swell; excess delays maturity.
Stop Bolting Before it Starts
Bolting turns sweet flesh spicy and halves storage life. Triggers are temperature swings below 45 °F after the plant has six true leaves, or drought during bulb initiation. Keep a floating row cover handy during late cold snaps, mulch to smooth soil temperature, and never let seedlings sit in six-packs too long before transplanting.
Managing Weeds
Onion leaves are wimpy competitors. Shallow hoeing or a 2 in straw mulch blocks weeds and keeps soil cool. Do not pile mulch against necks; rot sets in fast.
Companion Planting & Rotation
Carrots, lettuce, and beets share light footprints and do not bully for space. Avoid beans and peas; onions stunt legume roots. Rotate away from all alliums (garlic, leeks) for three years to curb onion maggot and pink root disease.
Organic Pest Patrol
Onion thrips rasp leaf surfaces, leaving silvery streaks. Blast with water at dawn; release predatory mites or spray insecticidal soap weekly until damage stops. Reflective silver mulch confuses adults.
Onion maggot larvae burrow into the base, wilting plants. Row covers during fly flight (May–June, August) and beneficial nematodes watered into soil cut numbers. Never compost infected bulbs.
Cutworms: A 4 in cardboard collar around transplants at planting blocks night feeders.
Common Diseases & Fast Fixes
Purple blotch (Alternaria): Small brown flecks enlarge into purple-ringed spots. Improve air flow, water early, remove worst leaves, apply organic copper spray if lesions reach more than 25 % of foliage.
Downy mildew: Grey mold on leaf tips in cool, damp weather. Remove affected leaves, space wider next year, avoid overhead watering.
Pink root roots turn pink then black; no cure once infected. Plant resistant varieties (‘Toughball’) and rotate.
Predicting Harvest Time
80 % of the tops flop naturally—this is your cue. Over-watering after this stage risks bulb rot. Choose a sunny, breezy morning and gently lift with a fork 3 in behind each bulb. Shake soil free but do not wash.
Curing for Storage
Good curing seals necks and outer scales, preventing mold. Lay bulbs in a single layer on mesh trays or hang in bunches of five in an airy shed, 75–85 °F, for two to three weeks until necks rattle when pinched. Sun-scalding ruins flavor; work in shade.
Sorting for Longevity
After curing, clip roots and trim tops to 1 in. Store only firm, flawless bulbs with intact papery skins. Anything bruised goes to the kitchen first. The thicker the neck, the shorter the shelf life—use these within six weeks.
Storage Options
Braids: Beautiful but only for cool, dry kitchens; humidity invites mold.
Mesh bags: Hang in a dark basement at 35–45 °F with 65 % humidity. Check monthly and remove any that sprout or soften.
Freezing diced onions: No blanching needed; freeze flat on a tray, then bag. Flavor is fine for sautés, texture lost for salads.
Expect 6–12 months of shelf life for cured yellow keepers, 3–5 months for sweets like ‘Walla Walla’.
Seed Saving Basics
Onions are biennial. Replant 15–20 unharvested bulbs after winter, 12 in apart. The second spring each sends up a globe-shaped umbel. Isolate by one mile or bag blossoms with insect netting to keep varieties pure. Harvest seed heads when black seeds rattle inside capsules, dry another week indoors, then winnow. Viability drops after one year; share fresh seed with neighbors.
Quick Troubleshooting Chart
Leaves yellow early → Overwatering or nitrogen deficiency—check soil, adjust.
Bulbs split → Uneven watering—mulch and irrigate steadily.
Small bulbs → Planted too late, wrong day-length type, or crowded.
Takeaway Checklist
✓ Match variety to your day length.
✓ Use sets for speed, seeds for choice.
✓ Keep weeds down, moisture steady, nitrogen modest.
✓ Cure thoroughly for months of storage.
Grow one successful bed and store-bought onions will forever taste bland by comparison.
Disclaimer: This article was generated by an AI tool for informational purposes. Always follow local extension advice for pest regulations and fertilizer guidelines.